JP6935229B2 - Circularly polarizing film, circularly polarizing film with adhesive layer and image display device - Google Patents

Description

The present invention relates to a circularly polarizing film. The present invention also relates to a circularly polarizing film with an adhesive layer using the circularly polarizing film. Further, the present invention relates to an image display device using the circularly polarizing film or the circularly polarizing film with an adhesive layer. The circularly polarizing film of the present invention is suitably used for an image display device, and can be particularly preferably used for an image display device for visually recognizing a display screen through a polarizing lens such as polarized sunglasses.

In recent years, there have been increasing opportunities for image display devices to be used under strong external light, such as mobile phones, smartphones, tablet personal computers (PCs), car navigation systems, digital signage, and window displays. When the image display device is used outdoors in this way, when the viewer wears polarized sunglasses to view the image display device, the transmission axis direction of the polarized sunglasses and the emission of the image display device depend on the viewing angle of the viewer. The direction of the transmission axis on the side becomes a cross Nicol state, and as a result, the screen becomes black and the displayed image may not be visually recognized. In order to solve such a problem, a technique of arranging a circularly polarizing film (polarizing film for polarized sunglasses) on the visible side surface of an image display device has been proposed (Patent Document 1). Further, the image display device as described above is susceptible to external impacts such as dropping and collision, and the circularly polarizing film is also required to have impact resistance.

In addition, when an optical film such as a circularly polarizing film is attached to a liquid crystal cell or the like, the optical film is peeled off from the liquid crystal panel even if the bonding position is incorrect or a foreign substance is caught in the bonding surface. , Liquid crystal cells, etc. may be reused. In such a peeling step, re-peeling property (reworking property) capable of peeling the entire optical film from the liquid crystal panel without adhesive residue is required.

As the circularly polarizing film, a retardation film having a circularly polarizing function or an elliptically polarizing function may be used as a protective film provided on one of the polarizers. As the retardation film, a stretched polycarbonate film and a stretched norbornene-based polymer film are known. However, the polycarbonate film and the norbornene-based polymer film have low moisture permeability and have high dimensional stability in a humidity environment, which is good. On the other hand, when the polycarbonate film is used, the unevenness of the in-plane phase difference Re due to the large photoelastic coefficient occurs. There was a serious problem that it occurred. Further, when a norbornene-based film is used as the retardation film on the viewing side (further, on the viewing side than the polarizer) of the optical cell (for example, a liquid crystal cell), sebum or detergent may adhere to the norbornene-based film. There is a serious problem that the norbornene-based film is cracked or dissolved by the solvent contained in the interlayer resin when the circularly polarizing film is fully laminated.

On the other hand, as the retardation film of the circularly polarizing film, a cellulose ester film such as a cellulose acetate film or a cellulose acetate propionate film can be used. Since the cellulose ester film has a small photoelastic coefficient, unevenness of the in-plane retardation Re is less likely to occur, and it is possible to suppress the generation and dissolution of cracks even when it comes into contact with sebum, detergent, or solvent (patented). Document 2). Further, the retardation film obtained by stretching a cellulose ester film is usually used for TV, and the thickness thereof is generally 40 μm or more.

Japanese Unexamined Patent Publication No. 2014-16425 Japanese Unexamined Patent Publication No. 2016-177165

By the way, in recent years, image display devices are required to be thin, and the retardation film is also required to be thin. Further, since the retardation film is obtained by stretching treatment, curling is likely to occur, and thinning is required from the viewpoint of suppressing curling. However, the circularly polarizing film in which the retardation film obtained by stretching the cellulose ester film is bonded to the polarizer is in the vicinity of the surface where the retardation film and the polarizer are bonded at the time of external impact or rework. There was a problem that it was peeled off.

The present invention is a circularly polarizing film having a polarizing element, a retardation film arranged on one side of the polarizing element, and a protective layer arranged on the other side of the polarizing element, and is resistant to polarization. An object of the present invention is to provide a circularly polarizing film having excellent impact resistance and reworkability and capable of suppressing curling.

Another object of the present invention is to provide a circularly polarizing film with an adhesive layer using the circularly polarizing film, and further to provide an image display device using the circularly polarizing film or the circularly polarizing film with an adhesive layer. And.

As a result of diligent studies, the inventors of the present application have found that the above problems can be solved by the following circularly polarizing films and the like, and have arrived at the present invention.

That is, the present invention includes a polarizer, a retardation film arranged on one side of the polarizer, and a protective layer arranged on the other side of the polarizer.
The retardation film has a function of converting linearly polarized light into circularly polarized light or elliptically polarized light, has a thickness of 35 μm or less, and has a thickness of 35 μm or less.
When both sides of the retardation film have different fracture starting loads in the scratch test, the side with the higher fracture starting load is the first surface and the side with the lower fracture starting load is the second surface.
The polarizer relates to a circularly polarizing film, characterized in that it is bonded to the first surface of the retardation film.

In the circularly polarizing film, it is preferable that the fracture starting load of the first surface of the retardation film is 55 mN or more.

The circularly polarizing film may have a surface functional layer on the second surface of the retardation film.

In the circularly polarizing film, the angle formed by the absorption axis of the polarizer and the slow axis of the retardation film is preferably 35 ° to 55 °. When the circularly polarizing film has a long shape, the angle formed by the slow axis of the retardation film and the long direction is preferably 35 ° to 55 °.

In the circularly polarizing film, the retardation film is a stretched product of a resin film molded on a casting body by a solution casting method, and is suitable when the surface of the resin film on the casting body side is the first surface. Is.

In the circularly polarizing film, a cellulose ester-based film can be used as the retardation film.

In the circularly polarizing film, one in which the polarizer, the retardation film, and the protective layer are bonded to each other via an adhesive layer can be used.

The present invention also relates to the circularly polarizing film and the circularly polarizing film with an adhesive layer, which comprises the pressure-sensitive adhesive layer.

Further, the present invention is characterized in that a circularly polarizing film or a circularly polarizing film with an adhesive layer is provided on the viewing side of the optical cell, and the retardation film is arranged on the viewing side of the polarizer. Regarding the device.

For polycarbonate films and norbornene-based polymer films, a molding method by a melt extrusion method is generally used, and there is no difference in physical properties on both sides of the film obtained by such a film forming method. On the other hand, as a cellulose ester film, a film forming method using a solution casting method is generally used. In the solution casting method, a resin solution (dope) is poured onto a drum (casting drum) or a stainless steel smooth belt with a smooth surface to adhere to it, and the solvent is evaporated through a process of heating this to form a film. do. In such a solution casting method, desolvation proceeds quickly on the side not in contact with the belt or drum surface (air side), so that the air side is in contact with the belt or drum surface, especially when molding a thin film. It is easier to harden than the side that is on the surface (there is something like a skin burr on the surface). As a result, it was found that the films obtained by the solution casting method had different physical properties on both sides. It was also found that when the film obtained by the solution casting method was bonded to another film, the air side was bonded for convenience.

Further, the retardation film used for the circularly polarizing film is obtained by diagonally stretching the film so that the angle between the width direction and the in-plane slow axis is within a predetermined range. Therefore, when the films having different physical characteristics on both sides are subjected to high stretching by the diagonal stretching, the air side of the obtained retardation film is mechanically more brittle than the opposite surface. It turned out. In particular, in the case of a thin film, the mechanical characteristics on the air side are fragile. As a result, it is presumed that when the thin retardation film was attached to the polarizer, peeling occurred at the time of impact or rework.

Based on the above findings, in the circularly polarizing film of the present invention, when a retardation film having different physical characteristics on both sides (having a function of converting linearly polarized light into circularly polarized light or elliptically polarized light) is arranged on the polarizer, the above-mentioned retardation is obtained. In the film, the side having strong mechanical characteristics, that is, the side having the high breaking start load in the scratch test was used as an index, and the side having the high breaking starting load was bonded to the polarizer. Thinning the film is not preferable from the viewpoint of impact resistance and reworkability, but in the present invention, when a retardation film having a thickness of 35 μm or less is used by adopting such a configuration. However, it is possible to provide a circularly polarizing film having excellent impact resistance and reworkability, because cohesive fracture in the vicinity of the surface where the retardation film and the polarizer are bonded is less likely to occur even at the time of impact or rework. Further, in the present invention, curling can be suppressed by using a retardation film having a thickness of 35 μm or less.

It is a schematic cross-sectional view which shows an example of the structural cross section of the circularly polarizing film of this invention. It is an image which shows the scratch mark before the fracture start (non-destruction part) of the measurement of the fracture start load. It is an image which shows the scratch mark at the fracture start point of the measurement of the fracture start load.

(Definition of terms and symbols)
Definitions of terms and symbols herein are as follows.
(1) Refractive index (nx, ny, nz)
"Nx" is the refractive index in the direction in which the in-plane refractive index is maximized (that is, the slow-phase axis direction), and "ny" is the in-plane direction orthogonal to the slow-phase axis (that is, the phase-advance axis direction). Is the refractive index of, and "nz" is the refractive index in the thickness direction.
(2) In-plane phase difference (Re)
“Re (λ)” is the in-plane phase difference of the film measured with light having a wavelength of λ nm at 23 ° C. For example, "Re (450)" is an in-plane phase difference of a film measured with light having a wavelength of 450 nm at 23 ° C. Re (λ) is obtained by the formula: Re = (nx−ny) × d, where d (nm) is the thickness of the film.
(3) Phase difference in the thickness direction (Rth)
“Rth (λ)” is the phase difference in the thickness direction of the film measured with light having a wavelength of 550 nm at 23 ° C. For example, "Rth (450)" is a phase difference in the thickness direction of a film measured with light having a wavelength of 450 nm at 23 ° C. Rth (λ) is obtained by the formula: Rth = (nx−nz) × d, where d (nm) is the thickness of the film.
(4) Nz coefficient The Nz coefficient is obtained by Nz = Rth / Re.
(5) Substantially Orthogonal or Parallel The expressions "substantially orthogonal" and "substantially orthogonal" include the case where the angle between the two directions is 90 ° ± 10 °, preferably 90 ° ± 7 °. It is more preferably 90 ° ± 5 °. The expressions "substantially parallel" and "substantially parallel" include the case where the angle between the two directions is 0 ° ± 10 °, preferably 0 ° ± 7 °, and even more preferably 0 ° ±. It is 5 °. Further, the term "orthogonal" or "parallel" in the present specification may include substantially orthogonal or substantially parallel states.
(6) Angle When referring to an angle in the present specification, the angle includes an angle in both clockwise and counterclockwise directions unless otherwise specified.
(7) Elongated shape "Long-shaped" means an elongated shape whose length is sufficiently long with respect to the width, for example, an elongated shape having a length of 10 times or more, preferably 20 times or more with respect to the width. Including shape.

<Overall composition of polarizing film>
FIG. 1 is a schematic cross-sectional view showing an example of a structural cross section of the circularly polarizing film of the present invention. The circularly polarizing film F of FIG. 1 includes a polarizing element 1, a retardation film 2 arranged on one side of the polarizing element 1, and a protective layer 3 arranged on the other side of the polarizing element 1. The retardation film 2 has a function of converting linearly polarized light into circularly polarized light or elliptically polarized light. Therefore, the circularly polarizing film of the present invention means a circularly polarizing film or an elliptically polarizing film. The circularly polarizing film F is typically arranged on the visual side of the image display device. In this case, the retardation film 2 is arranged so as to be on the viewing side. With the above configuration, excellent visibility can be realized even when the display screen is visually recognized through a polarized lens such as polarized sunglasses. Therefore, the circularly polarizing film F can also be suitably applied to an image display device that can be used outdoors.

As the retardation film 2, those having different fracture starting loads in the scratch test on both sides are used. In the retardation film 2, the side where the fracture start load is high is referred to as the first surface 2a, and the side where the fracture start load is low is referred to as the second surface 2b. As shown in FIG. 1, the polarizer 1 is bonded to the side of the first surface 2a of the retardation film 2.

If necessary, the circularly polarizing film F may further include a surface functional layer 4 on the second surface 2b (opposite side of the polarizer 1) of the retardation film 2. Further, the circularly polarizing film F may include another retardation film (not shown). The number of different retardation films, the arrangement position, the optical characteristics (for example, refractive index ellipsoid, in-plane retardation, thickness direction retardation, wavelength dispersion characteristics), mechanical characteristics, etc. can be appropriately set according to the purpose. ..

The polarizer 1 and the retardation film 2 are laminated so that the absorption axis of the polarizer 1 and the slow axis of the retardation film 2 form a predetermined angle. The angle formed by the absorption axis of the polarizer 1 and the slow axis of the retardation film 2 is preferably 35 ° to 55 °, more preferably 38 ° to 52 °, and even more preferably 40 ° to 50 °. , Especially preferably 42 ° to 48 °, and particularly preferably in the vicinity of 45 °. By arranging the retardation film 2 on the viewing side of the polarizer 1 in such an axial relationship, excellent visibility can be realized even when the display screen is visually recognized through a polarizing lens such as polarized sunglasses. can. Therefore, the polarizing film according to the embodiment of the present invention can be suitably applied to an image display device that can be used outdoors.

The circularly polarizing film F may have a single-wafer shape or a long shape (for example, a roll shape). When the circularly polarizing film F has an elongated shape, the absorption axis direction of the elongated polarizing element may be the elongated direction or the width direction. Preferably, the absorption axis direction of the polarizer is a long direction. This is because the polarizer is easy to manufacture, and as a result, the manufacturing efficiency of the circularly polarizing film is excellent. When the circularly polarizing film has a long shape, the angle θ formed by the slow axis of the retardation film 2 and the long direction is preferably 35 ° to 55 °, more preferably 38 ° to 52 °, and further. It is preferably 40 ° to 50 °, particularly preferably 42 ° to 48 °, and particularly preferably in the vicinity of 45 °. As will be described later, by forming the retardation film constituting the retardation film by oblique stretching, it is possible to form a long retardation film (phase difference film) having a slow axis in the oblique direction. As a result, a long circularly polarizing film can be realized. Since such a long circularly polarizing film can be produced by roll-to-roll, the productivity is remarkably excellent.

The overall thickness of the circularly polarizing film is typically 40 μm to 300 μm, preferably 40 μm to 160 μm, more preferably 50 μm to 140 μm, and even more preferably 60 μm to 120 μm. According to the embodiment of the present invention, it is possible to obtain a circularly polarizing film having such a very thin thickness and well suppressed curl. The total thickness of the circularly polarizing film refers to the total thickness of the polarizer, the retardation film, the protective layer, the surface functional layer if present, and the adhesive layer for laminating them.

Hereinafter, each layer constituting the circularly polarizing film according to the embodiment of the present invention will be described.

<Polarizer>
As the polarizer 1, any suitable polarizer can be adopted. For example, the resin film forming the polarizer may be a single-layer resin film or a laminated body having two or more layers.

Specific examples of the polarizer composed of a single-layer resin film include highly hydrophilic films such as polyvinyl alcohol (PVA) -based resin films, partially formalized PVA-based resin films, and ethylene / vinyl acetate copolymerization-based partially saponified films. Examples include molecular films that have been dyed and stretched with bicolor substances such as iodine and bicolor dyes, and polyene-based oriented films such as PVA dehydrated products and polyvinyl chloride dehydrogenated products. Be done. Preferably, since the PVA-based resin film is excellent in optical characteristics, a polarizer obtained by dyeing a PVA-based resin film with iodine and uniaxially stretching the film is used.

The dyeing with iodine is performed, for example, by immersing a PVA-based resin film in an aqueous iodine solution. The draw ratio of the uniaxial stretching is preferably 3 to 7 times. Stretching may be performed after the dyeing treatment or while dyeing. Alternatively, it may be stretched and then dyed. If necessary, the PVA-based resin film is subjected to a swelling treatment, a cross-linking treatment, a cleaning treatment, a drying treatment and the like. For example, by immersing the PVA-based resin film in water and washing it with water before dyeing, not only can the dirt and blocking inhibitor on the surface of the PVA-based resin film be washed, but also the PVA-based resin film is swollen and dyed. It is possible to prevent unevenness and the like.

Specific examples of the polarizer obtained by using the laminate include a laminate of a resin base material and a PVA-based resin layer (PVA-based resin film) laminated on the resin base material, or a resin base material and the resin. Examples thereof include a polarizer obtained by using a laminate with a PVA-based resin layer coated and formed on a base material. The polarizer obtained by using the laminate of the resin base material and the PVA-based resin layer coated and formed on the resin base material is, for example, a resin base material obtained by applying a PVA-based resin solution to the resin base material and drying the resin base material. It is produced by forming a PVA-based resin layer on the PVA-based resin layer to obtain a laminate of a resin base material and a PVA-based resin layer; stretching and dyeing the laminate to make the PVA-based resin layer a polarizer. obtain. In the present embodiment, stretching typically includes immersing the laminate in an aqueous boric acid solution for stretching. Further, stretching may further include, if necessary, stretching the laminate in the air at a high temperature (eg, 95 ° C. or higher) prior to stretching in boric acid aqueous solution. The obtained resin substrate / polarizer laminate may be used as it is (that is, the resin substrate may be used as a protective layer for the polarizer), and the resin substrate is peeled off from the resin substrate / polarizer laminate. Then, an arbitrary appropriate protective layer according to the purpose may be laminated on the peeled surface. Details of the method for producing such a polarizer are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. The entire description of the publication is incorporated herein by reference.

The thickness of the polarizer is preferably 15 μm or less, more preferably 13 μm or less, still more preferably 10 μm, and particularly preferably 8 μm or less. The lower limit of the thickness of the polarizer is 2 μm in one embodiment and 3 μm in another embodiment. According to the embodiment of the present invention, even though the thickness of the polarizer is so thin, curling when the polarizing film is heated can be satisfactorily suppressed.

The polarizer preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The simple substance transmittance of the polarizer is preferably 42.0% to 45.5%, more preferably 42.5% to 45.0%. According to the present invention, it is possible to realize a polarizing film that is extremely thin and has curl suppressed, and further, it is possible to realize the above-mentioned excellent single transmittance in such a polarizing film.

The degree of polarization of the polarizer is 98% or more, preferably 98.5% or more, and more preferably 99% or more as described above. According to the present invention, it is possible to realize a polarizing film that is extremely thin and has curl suppressed, and further, it is possible to realize the above-mentioned excellent degree of polarization in such a polarizing film.

<Phase difference film>
As described above, the retardation film 2 has a function of converting linearly polarized light into circularly polarized light or elliptically polarized light. That is, the retardation film 2 typically shows a relationship in which the refractive index characteristics are nx> ny. The in-plane retardation Re (550) of the retardation film is preferably 80 nm to 160 nm, more preferably 90 nm to 120 nm. When the in-plane retardation is in such a range, a retardation film having appropriate elliptically polarized light performance can be obtained with excellent productivity and reasonable cost. As a result, a polarizing film capable of ensuring good visibility even when the display screen is visually recognized through a polarizing lens such as polarized sunglasses can be obtained with excellent productivity and reasonable cost.

The retardation film 2 shows any suitable refractive index ellipsoid as long as it has a relationship of nx> ny. Preferably, the refractive index ellipsoid of the retardation film shows a relationship of nx> ny ≧ nz. The Nz coefficient of the retardation film is preferably 1 to 2, more preferably 1 to 1.5, and even more preferably 1 to 1.3.

The retardation film 2 is composed of any suitable retardation film that can satisfy the above optical characteristics. Further, as the retardation film 2, those having different fracture starting loads in the scratch test on both sides are used. As described above, in the retardation film 2, the side where the fracture start load is high is the first surface 2a, and the side where the fracture start load is low is the second surface 2b. The fracture starting load of the first surface 2a is preferably 55 mN or more. When the fracture starting load satisfies 55 mN or more, cohesive fracture near the surface of the first surface 2a is unlikely to occur, and the impact resistance and reworkability of the circularly polarizing film obtained by bonding to the polarizer are satisfied. Is preferable. The fracture starting load of the first surface 2a is preferably 58 mN or more, more preferably 60 mN or more, and further preferably 70 mN or more.

A typical example of the resin forming the retardation film is a cellulose ester resin (hereinafter, also simply referred to as a cellulose ester).

Specific examples of the cellulose ester include cellulose (di, tri) acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, and cellulose phthalate. Preferably, it is cellulose triacetate, cellulose diacetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, or cellulose acetate butyrate. Cellulose esters may be used alone or in combination.

In the cellulose ester, a part or all of the free hydroxyl groups (hydroxyl groups) at the 2, 3, and 6 positions in the glucose unit constituting the cellulose by β-1,4-glycoside bond is an acyl group such as an acetyl group or a propionyl group. It is a polymer esterified by. Here, the "acyl group substitution degree" represents the total ratio of the hydroxyl groups esterified at the 2, 3, and 6 positions of the repeating unit glucose. Specifically, the degree of substitution is 1 when the hydroxyl groups at the 2-position, 3-position, and 6-position of cellulose are 100% esterified. Therefore, when all of the 2-positions, 3-positions and 6-positions of cellulose are 100% esterified, the degree of substitution is 3 at the maximum. Further, the "average acyl group substitution degree" means an acyl group substitution degree in which the acyl group substitution degree of a plurality of glucose units constituting the cellulose ester resin is expressed as an average value per unit. The degree of acyl group substitution can be measured according to ASTM-D817-96.

Examples of the acyl group include an acetyl group, a propionyl group, a butanoyl group, a heptanoil group, a hexanoyl group, an octanoyl group, a decanoyl group, a dodecanoyl group, a tridecanoyl group, a tetradecanoyl group, a hexadecanoyl group, an octadecanoyl group and an isobutanoyl group. Examples thereof include a group, a tert-butanoyl group, a cyclohexanecarbonyl group, an oleoil group, a benzoyl group, a naphthylcarbonyl group and a cinnamoyl group.

In one embodiment, when the degree of acetyl group substitution of the cellulose ester resin is X and the degree of propionyl group substitution is Y, it is preferable that X and Y satisfy the following formulas (1) and (2).
Equation (1): 2.0 ≤ (X + Y) ≤ 2.8
Equation (2): 0 ≤ Y ≤ 1.0
More preferably, the cellulose ester resin satisfying the above formulas (1) and (2) is a cellulose ester resin satisfying the following formulas (1a) and (2), and a cellulose ester resin satisfying the following formula (1b). , Contain.
Equation (1a): 2.0 ≦ (X + Y) <2.5
Formula (1b): 2.5 ≦ (X + Y) ≦ 2.8 “Acetyl group substitution degree” and “propionyl group substitution degree” are more specific indexes of the above acyl group substitution degree, and are “acetyl”. The "group substitution degree" represents the total ratio of hydroxyl groups esterified by acetyl groups at the 2, 3, and 6 positions of glucose in the repeating unit, and the "propionyl group substitution degree" is the repeating unit. It represents the sum of the proportions of hydroxyl groups esterified by acetyl groups at the 2-position, 3-position and 6-position of glucose.

The cellulose ester resin has a molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) preferably 1.5 to 5.5, more preferably 2.0 to 5.0, and even more preferably 2.5. It is ~ 5.0, and particularly preferably 3.0 to 5.0.

Any suitable cellulose can be used as the cellulose as the raw material of the cellulose ester resin. Specific examples include cotton linter, wood pulp, and kenaf. Cellulose ester resins obtained from different raw materials may be used in combination.

The cellulose ester resin can be produced by any suitable method. Representative examples include methods involving the following procedures: raw material cellulose, certain organic acids (eg, acetic acid, propionic acid), acid anhydrides (eg, acetic anhydride, propionic anhydride), and catalysts (eg, acetic anhydride, propionic anhydride). Sulfate) is mixed to esterify the cellulose and the reaction proceeds until a cellulose triester is obtained. In the cellulose triester, the three hydroxyl groups (hydroxyl groups) of the glucose unit are replaced with the acyl acid of the organic acid. By using two kinds of organic acids at the same time, a mixed ester type cellulose ester (for example, cellulose acetate propionate and cellulose acetate butyrate) can be prepared. The cellulose ester is then hydrolyzed to synthesize a cellulose ester with the desired degree of acyl group substitution. Then, a cellulose ester resin can be obtained through steps such as filtration, precipitation, washing with water, dehydration, and drying.

The retardation film 2 (phase difference film) is typically produced by stretching a resin film formed of the above-mentioned resin in at least one direction.

Any suitable method can be adopted as the method for forming the resin film. For example, a melt extrusion method (for example, T die molding method), a cast coating method (for example, a casting method), a calendar molding method, a hot pressing method, a co-extrusion method, a co-melt method, multi-layer extrusion, an inflation molding method and the like can be mentioned. Be done. Preferably, a T-die molding method, a casting method and an inflation molding method are used.

As the resin film used for the retardation film used in the present invention (those having different fracture starting loads in the scratch test on both sides), those obtained by the solution casting method are preferably used. In the solution casting method, a resin solution (dope) is poured onto a casting body (casting drum or a stainless steel smoothing belt) having a smooth surface to adhere to the film, and the solvent is evaporated through a step of heating the casting body (casting drum or a stainless steel smoothing belt) to evaporate the film. Mold. In such a solution casting method, the desolvation proceeds faster on the side not in contact with the casting body (air side), so that the breaking start load of the obtained resin film is smaller on the air side than on the casting body side. In the retardation film obtained by stretching the resin film obtained by the solution casting method, the surface of the resin film on the casting body side becomes the first surface.

The thickness of the resin film (unstretched film) can be set to an arbitrary appropriate value according to desired optical characteristics, stretching conditions described later, and the like. It is preferably 50 μm to 250 μm, and more preferably 80 μm to 200 μm.

Any suitable stretching method and stretching conditions (for example, stretching temperature, stretching ratio, stretching direction) can be adopted for the stretching. Specifically, various stretching methods such as free-end stretching, fixed-end stretching / free-end contraction, and fixed-end contraction can be used alone or simultaneously or sequentially. As for the stretching direction, it can be performed in various directions and dimensions such as a horizontal direction, a vertical direction, a thickness direction, and a diagonal direction. The stretching temperature is preferably in the range of the glass transition temperature (Tg) of the resin film ± 20 ° C.

By appropriately selecting the stretching method and stretching conditions, a retardation film having the desired optical characteristics (for example, refractive index ellipsoid, in-plane retardation, Nz coefficient) (as a result, a retardation film) can be obtained. Can be done.

In one embodiment, the retardation film 2 is produced by uniaxially stretching or fixed-end uniaxially stretching the resin film. Specific examples of the uniaxial stretching include a method of stretching the resin film in the longitudinal direction (longitudinal direction) while running the resin film in the long direction. Another specific example of uniaxial stretching is a method of stretching in the lateral direction using a tenter. The draw ratio is preferably 10% to 500%.

In another embodiment, the retardation film 2 is produced by continuously obliquely stretching a long resin film in a direction of an angle θ with respect to a long direction. By adopting oblique stretching, a long stretched film having an orientation angle of an angle θ with respect to the long direction of the film can be obtained. Can be simplified. The angle θ is as described above.

Examples of the stretching machine used for diagonal stretching include a tenter type stretching machine capable of applying a feeding force, a pulling force, or a pulling force at different speeds in the horizontal and / or vertical directions. The tenter type stretching machine includes a horizontal uniaxial stretching machine, a simultaneous biaxial stretching machine, and the like, but any suitable stretching machine can be used as long as the long resin film can be continuously and diagonally stretched.

Examples of the method of diagonal stretching include JP-A-50-83482, JP-A-2-113920, JP-A-3-182701, JP-A-2000-9912, and JP-A-2002-86554. Examples thereof include the methods described in JP-A-2002-22944.

The thickness of the retardation film (for example, the stretched film) is 35 μm or less. As the thickness increases, shrinkage and expansion tend to increase, and when the thickness exceeds 40 μm, the amount of panel warpage (curl) in terms of heat and humidity reliability increases. The thickness is preferably 38 μm or less, and more preferably 35 μm or less. On the other hand, when the thickness becomes thin, the load becomes low even on the surface (first surface) where the fracture starting load is large, and the peeling force decreases. Therefore, the thickness is preferably 15 μm or more, and more preferably 20 μm or more. Is preferable.

As the retardation film constituting the retardation film 2, a commercially available film may be used as it is as long as it satisfies the requirements of the present invention, and the commercially available film is subjected to secondary processing (for example, stretching) according to the purpose. Treatment, surface treatment) may be used.

The surface of the retardation film 2 on the polarizer 1 side may be surface-treated. Examples of the surface treatment include corona treatment, plasma treatment, frame treatment, primer coating treatment, and saponification treatment. Examples of the corona treatment include a method of discharging in normal pressure air by a corona treatment machine. As the plasma treatment, for example, a method of discharging in normal pressure air by a plasma discharger can be mentioned. Examples of the frame processing include a method in which a flame is brought into direct contact with the film surface. Examples of the primer coating treatment include a method in which an isocyanate compound, a silane coupling agent, or the like is diluted with a solvent, and the diluted solution is thinly coated. Examples of the saponification treatment include a method of immersing in an aqueous sodium hydroxide solution. Preferred are corona treatment and plasma treatment.

<Protective layer>
The protective layer 3 is formed of any suitable film that can be used as a protective layer for the polarizer. Specific examples of the material that is the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based materials such as polyethylene terephthalate and polyethylene naphthalate, polyvinyl alcohol-based materials, polycarbonate-based materials, nylon and aromatic polyamides. Polyamide-based, polyimide-based, polyethersulfone-based, polysulfone-based, polystyrene-based, polynorbornene-based, polyolefin-based such as ethylene / propylene copolymer, cyclo-based or cyclic olefin-based having a norbornene structure, (meth) acrylic-based , Acetate-based transparent resin and the like. Further, thermosetting resins such as (meth) acrylic, urethane, (meth) acrylic urethane, epoxy, and silicone, or ultraviolet curable resins can also be mentioned. In addition to this, for example, glassy polymers such as siloxane-based polymers can also be mentioned.

As the (meth) acrylic resin, Tg (glass transition temperature) is preferably 115 ° C. or higher, more preferably 120 ° C. or higher, still more preferably 125 ° C. or higher, and particularly preferably 130 ° C. or higher. This is because it can be excellent in durability. The upper limit of Tg of the (meth) acrylic resin is not particularly limited, but is preferably 170 ° C. or lower from the viewpoint of moldability and the like.

As the (meth) acrylic resin, any suitable (meth) acrylic resin can be adopted as long as the effects of the present invention are not impaired. For example, poly (meth) acrylic acid esters such as polymethyl methacrylate, methyl methacrylate- (meth) acrylic acid copolymers, methyl methacrylate- (meth) acrylic acid ester copolymers, methyl methacrylate-acrylic acid esters. -(Meta) acrylate copolymer, (meth) methyl acrylate-styrene copolymer (MS resin, etc.), polymer having alicyclic hydrocarbon group (for example, methyl methacrylate-cyclohexyl methacrylate copolymer) , Methyl methacrylate- (meth) norbornyl acrylate copolymer, etc.). _{Preferred are C 1-6} alkyl poly (meth) acrylates such as methyl poly (meth) acrylate. More preferably, a methyl methacrylate-based resin containing methyl methacrylate as a main component (50 to 100% by weight, preferably 70 to 100% by weight) can be mentioned.

Specific examples of the above (meth) acrylic resin include, for example, Acrypet VH and Acrypet VRL20A manufactured by Mitsubishi Rayon Co., Ltd., and a (meth) acrylic resin having a ring structure in the molecule described in JP-A-2004-70296. Examples thereof include resins, high Tg (meth) acrylic resins obtained by intramolecular cross-linking and intramolecular cyclization reactions.

As the (meth) acrylic resin, a (meth) acrylic resin having a lactone ring structure is particularly preferable in that it has high heat resistance, high transparency, and high mechanical strength.

Examples of the (meth) acrylic resin having the lactone ring structure include JP-A-2000-230016, JP-A-2001-151814, JP-A-2002-120326, JP-A-2002-254544, and JP-A-2005. Examples thereof include (meth) acrylic resins having a lactone ring structure described in JP-A-146084.

The (meth) acrylic resin having the lactone ring structure has a mass average molecular weight (sometimes referred to as a weight average molecular weight) of preferably 1000 to 2000000, more preferably 5000 to 1000000, still more preferably 1000 to 500000, particularly. It is preferably 50,000 to 500,000.

The (meth) acrylic resin having the lactone ring structure has a Tg (glass transition temperature) of preferably 115 ° C. or higher, more preferably 125 ° C. or higher, still more preferably 130 ° C. or higher, particularly preferably 135 ° C., most preferably. Is 140 ° C. or higher. This is because it can be excellent in durability. The upper limit of Tg of the (meth) acrylic resin having a lactone ring structure is not particularly limited, but is preferably 170 ° C. or lower from the viewpoint of moldability and the like.

In addition, in this specification, "(meth) acrylic type" means an acrylic type and / or a methacryl type.

The protective layer 3 is preferably optically isotropic. As used herein, "optically isotropic" means that the in-plane retardation Re (550) is 0 nm to 10 nm and the thickness direction retardation Rth (550) is -10 nm to +10 nm. say.

The thickness of the protective layer is preferably 5 μm to 60 μm, more preferably 10 μm to 40 μm.

<Surface functional layer>
A surface functional layer 4 can be provided on the second surface of the retardation film 2. Examples of the surface functional layer include a hard coat layer, an antireflection layer, a sticking prevention layer, a diffusion layer and an antiglare layer. The functional layers such as the hard coat layer, the antireflection layer, the sticking prevention layer, the diffusion layer and the antiglare layer can be provided on the retardation film itself, and are separately provided separately from the retardation film. You can also do it.

As the surface functional layer, for example, a hard coat layer is preferably applied. The hard coat layer has a function of imparting chemical resistance, scratch resistance and surface smoothness to the circularly polarizing film and improving dimensional stability under high temperature and high humidity. Any suitable configuration can be adopted as the hard coat layer. The hard coat layer is, for example, a cured layer of any suitable UV curable resin. Examples of the ultraviolet curable resin include acrylic resin, silicone resin, polyester resin, urethane resin, amide resin, epoxy resin and the like. The glass transition temperature of the resin constituting the hard coat layer is preferably 120 ° C. to 300 ° C., more preferably 130 ° C. to 250 ° C. Within such a range, a polarizing film having excellent dimensional stability at high temperatures can be obtained. The hard coat layer may optionally contain any suitable additive. Typical examples of the additive include inorganic fine particles and / or organic fine particles.

The details of the hard coat layer are described in, for example, Japanese Patent Application Laid-Open No. 2007-171943, and the description thereof is incorporated herein by reference.

The thickness of the surface functional layer 4 is preferably 10 μm or less, more preferably 1 μm to 8 μm, and further preferably 2 μm to 7 μm.

<Adhesive layer>
Any suitable adhesive layer (not shown) is used for bonding the layers constituting the circularly polarizing film according to the embodiment of the present invention. The adhesive layer may be an adhesive layer or an adhesive layer. The adhesive layer is formed by the adhesive. The type of adhesive is not particularly limited, and various adhesives can be used. The adhesive layer is not particularly limited as long as it is optically transparent, and various forms such as water-based, solvent-based, hot-melt-based, and active energy ray-curable type are used as the adhesive. Alternatively, an active energy ray-curable adhesive is suitable.

Typically, the polarizer 1 and the retardation film 2 and the protective layer 3 are bonded to each other with a water-based adhesive. As the water-based adhesive, any suitable water-based adhesive can be adopted. Preferably, a water-based adhesive containing a PVA-based resin is used. The average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably about 100 to 5500, more preferably 1000 to 4500, from the viewpoint of adhesiveness. The average degree of saponification is preferably about 85 mol% to 100 mol%, more preferably 90 mol% to 100 mol% from the viewpoint of adhesiveness.

The PVA-based resin contained in the water-based adhesive preferably contains an acetoacetyl group. This is because the adhesion between the polarizer and the retardation film and the protective layer is excellent, and the durability can be excellent. The acetoacetyl group-containing PVA-based resin can be obtained, for example, by reacting the PVA-based resin with diketene by an arbitrary method. The degree of acetoacetyl group modification of the acetoacetyl group-containing PVA resin is typically 0.1 mol% or more, preferably about 0.1 mol% to 40 mol%, and more preferably 1 mol% to 20 mol. %, Especially preferably 1 mol% to 7 mol%. The degree of acetoacetyl group modification is a value measured by NMR.

The solid content concentration of the water-based adhesive is preferably 6% by weight or less, more preferably 0.1% by weight to 6% by weight, and further preferably 0.5% by weight to 6% by weight. When the solid content concentration is in such a range, there is an advantage that the dimensional control rate of the polarizing plate can be easily controlled. If the solid content concentration is too low, the water content of the obtained polarizing film increases, and the dimensional change may become large depending on the drying conditions. If the solid content concentration is too high, the viscosity of the adhesive may be high, and the productivity of the polarizing film may be insufficient.

The thickness of the adhesive layer is preferably 0.01 μm to 7 μm, more preferably 0.05 μm to 5 μm, still more preferably 0.05 μm to 2 μm, and particularly preferably 0.1 μm to 1 μm. If the thickness of the adhesive layer is too thin, the cohesive force of the adhesive itself cannot be obtained, and the adhesive strength may not be obtained. If the thickness of the adhesive layer is too thick, the circularly polarizing film may not be able to satisfy the durability.

Adhesive layers can be provided on one or both sides of the circularly polarizing film F (not shown). For example, since the pressure-sensitive adhesive layer is provided in advance on the protective layer 3 side of the circularly polarizing film F, it can be easily attached to another optical member (for example, a liquid crystal cell or an organic EL panel). It is preferable that a release film is adhered to the surface of the pressure-sensitive adhesive layer until it is used. On the other hand, the adhesive layer on the visual side (phase difference film 2 side) is suitable for, for example, an input device such as a touch panel applied on the visual side of an image display device, and a member such as a transparent substrate such as a cover glass or a plastic cover. Can be applied.

<Manufacturing method of circularly polarizing film>
Only the characteristic parts of an example of the method for producing a circularly polarizing film according to the embodiment of the present invention will be briefly described. In this manufacturing method, a laminate having a retarder 1 and a retardation film 2 arranged on one side of the polarizer 1 and a protective layer 3 arranged on the other side of the polarizer 1 is produced. In addition, heating the laminate at a temperature of, for example, 85 ° C. or higher (hereinafter, may be referred to as high temperature heating) is included. The heating temperature of high temperature heating is preferably 86 ° C. or higher. The upper limit of the heating temperature for high-temperature heating is, for example, 100 ° C. The heating time for high-temperature heating is preferably 3 to 10 minutes, more preferably 3 to 6 minutes. The laminate may be heated at a temperature below 85 ° C. (low temperature heating) before and / or after high temperature heating. The heating temperature and heating time for bass heating can be set appropriately depending on the intended purpose and the desired properties of the resulting polarizing film. The high temperature heating and / or low temperature heating may also serve as a drying treatment of the adhesive in laminating the polarizer, the retardation film (phase difference film) and the protective layer (protection film). As the method for forming the polarizer, the retardation film (phase difference film) and the protective layer (protection film), the above-mentioned method or any appropriate method can be adopted. As for the method of laminating the polarizer, the retardation film (phase difference film) and the protective layer (protection film), any suitable method can be adopted.

<Image display device>
The image display device according to the embodiment of the present invention includes a circularly polarizing film on the visual side of the optical cell. The circularly polarizing film is arranged so that the retardation film is on the visual side of the polarizer. Typical examples of an image display device including an optical cell include a liquid crystal display device and an organic electroluminescence (EL) display device. By providing the above-mentioned polarizing film on the viewing side, such an image display device can realize excellent visibility even when the display screen is visually recognized through a polarizing lens such as polarized sunglasses. Therefore, such an image display device can be suitably used outdoors.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The evaluation items in the examples are as follows.

<Fracture start load>
As a device for measuring the fracture starting load, a nanoscratch tester manufactured by CSM Instruments SA was used. The first surface or the second surface of each retardation film (sample) was attached to a slide glass, and the other surface (second surface or the first surface) was turned upward and fixed to the stage of the measuring device. Then, under a measurement environment of 23 ° C. and 50% RH, a cantilever ST-150 equipped with a conical diamond indenter (curvature radius of the tip of 10 μm) was used to load the device from 0 to 300 mN in the continuous load mode. A scratch test was conducted in which the (scratch load) was increased and scraped in one direction.
The scratch marks on the sample subjected to the scratch test were surface-observed with an objective lens 20 times using an optical microscope (manufactured by Nikon Corporation) attached to the apparatus. Then, the first point on the scratch mark where the back layer is peeled off longer than 2 μm in the scratch direction is set as the fracture start point, and the scratch load corresponding to the center of the length (fracture length) of the fracture start point with respect to the scratch direction is set. The load was used as the starting load for fracture. FIG. 2 is an image showing scratch marks before the start of fracture (non-destructive portion), and FIG. 3 is an image showing scratch marks at the start point of fracture.
As a result of measuring the above sample, the surface having a large fracture starting load was designated as the first surface, and the surface having a small fracture starting load was designated as the second surface. The results are shown in Table 1.

(Making a polarizer)
A polyvinyl alcohol film having a degree of polymerization of 2400, a degree of saponification of 99.9 mol%, and a thickness of 30 μm is immersed in warm water at 30 ° C., and the length of the polyvinyl alcohol film becomes 2.0 times the original length while being swollen. The uniaxial stretching was performed as described above. Next, the mixture of iodine and potassium iodide (weight ratio 0.5: 8) was immersed in an aqueous solution (dyeing bath) having a concentration of 0.3% by weight, and the length of the polyvinyl alcohol film was 3.0 times the original length. Staining was performed while uniaxially stretching so as to be. Then, while immersing in an aqueous solution of 5% by weight boric acid and 3% by weight of potassium iodide (crosslinked bath 1), the length of the polyvinyl alcohol film was stretched to be 3.7 times the original length, and then 60. The polyvinyl alcohol film was stretched in an aqueous solution (crosslinked bath 2) containing 4% by weight of boric acid and 5% by weight of potassium iodide at ° C. so that the length of the polyvinyl alcohol film was 6 times the original length. Then, after performing iodine ion impregnation treatment with an aqueous solution (iodine impregnation bath) of potassium iodide in an amount of 3% by weight, it was dried in an oven at 60 ° C. for 4 minutes to obtain an elongated (roll-shaped) polarizer. The thickness of the obtained polarizer was 12 μm. The absorption axis of the polarizer was parallel to the longitudinal direction.

(Phase difference film)
An elongated triacetyl cellulose (TAC) film obtained by a solution casting method was used as a diagonally stretched film. The thickness of the stretched film (stretched product of the TAC film) was 35 μm, 32 μm, 28 μm, 25 μm, 20 μm, and 40 μm, respectively.
Each stretched film (a stretched product of a TAC film) was provided with a hard coat layer having a thickness of 5 μm on each of the first surface or the second surface (the surface not bonded to the polarizer).
Each stretched film (stretched product of TAC film) was adjusted so that the in-plane retardation Re (550) was 105 nm, and the angle formed by the slow axis and the elongated direction was 45 °. ..

(Protective layer: protective film)
A long cycloolefin (COP) film (thickness 13 μm, trade name: ZF14-013, manufactured by Nippon Zeon Corporation) was used.

(Preparation of water-based adhesive)
A polyvinyl alcohol-based resin containing an acetoacetyl group (average degree of polymerization: 1200, saponification degree: 98.5 mol%, acetoacetylation degree: 5 mol%) was dissolved in pure water under a temperature condition of 30 ° C. A water-based adhesive was obtained by adjusting the solid content concentration to 4%.

Example 1
(Making a circularly polarizing film)
As the retardation film, a stretched film having a thickness of 35 μm (a stretched product of a TAC film) having a hard coat layer provided on the second surface was used. The first surface of the retardation film was coated with the water-based adhesive so that the thickness of the adhesive layer after drying was 80 nm. Similarly, the protective film was coated with the above-mentioned water-based adhesive so that the thickness of the adhesive layer after drying was 80 nm. Next, under the temperature condition of 23 ° C., the retardation film with the adhesive and the protective film were bonded to both sides of the polarizer with a roll machine, and then dried at 55 ° C. for 4 minutes and at 86 ° C. for 4 minutes to form a circle. A polarizing film was produced. The retarder, the retardation film with an adhesive, and the protective film were bonded so that the polarizer and the adhesive layer of the protective film were in contact with each other. In the obtained circularly polarizing film, the absorption axis direction of the polarizer was parallel to the elongated direction, and the angle formed by the slow axis of the retardation film and the elongated direction was 45 °.

Examples 2-5, Comparative Examples 1-7
In Example 1, the circularly polarizing film was prepared in the same manner as in Example 1 except that the thickness of the stretched film used for the retardation film and the surface on which the retardation film was attached to the polarizer were changed as shown in Table 1. Obtained.
The retardation films of the same thickness used in Examples 1 to 5 and Comparative Examples 1 to 5 are the same retardation films, and only the surfaces bonded to the polarizers are different. Further, the retardation films of the same thickness used in Comparative Example 6 and Comparative Example 7 are the same retardation films, and only the surface bonded to the polarizer is different.

Table 1 shows the following evaluations of the circularly polarizing films obtained in the above Examples and Comparative Examples.

<Peel force measurement method>
The peeling force of the obtained circularly polarizing film was measured by the following method.
A circularly polarizing film is cut into a size of 200 mm parallel to the stretching direction of the polarizer and 15 mm in the orthogonal direction, and a notch is made between the retardation film and the polarizer with a cutter knife to cut the retardation film side of the circularly polarizing film. It was attached to a glass plate. The protective film and the polarizer were peeled off at a peeling speed of 3000 mm / min in the 90-degree direction with Tencilon, and the peeling strength (N / 15 mm) was measured. The infrared absorption spectrum of the peeled surface after peeling was measured by the ATR method, and it was confirmed that the retardation film was agglomerated fracture (film fracture).
The peeling force is preferably 0.8 N / 15 mm or more, more preferably 1 N / 15 mm or more, and further preferably 1.5 N / 15 mm or more. In Table 1, the peel force of 0.8 N / 15 mm or more was designated as “◯”, and the peel force of less than 0.8 N / 15 was designated as “x”.
When the fracture starting load of the surface on which the retardation film is attached to the polarizer is 55 mN or more, the peeling force from the polarizer can be satisfied at 0.8 N / 15 mm.

<Length in curl direction>
The obtained circularly polarizing film was cut into a size of 112 mm × 65 mm (5 inch size) so that the absorption axis direction of the polarizer was the long side. The cut out circularly polarizing film was allowed to stand on a horizontal plane so that the hard coat layer was on the upper surface, and the height at which the end of the sample was curled and floated from the plane was measured. The case where the height (maximum floating height) of the largest floating portion was 3 mm or less was evaluated as ◯, and the case where the maximum floating height exceeded 3 mm was evaluated as x.

F circularly polarizing film 1 Polarizer 2 Phase difference film 3 Protective layer 4 Surface functional layer

Claims (10)

Comprising a polarizer, while a retardation film disposed on the side of the polarizer, and a protective layer disposed on the other side of the polarizer,
The retardation film has a function of converting linearly polarized light into circularly polarized light or elliptically polarized light, has a thickness of 35 μm or less, and has a thickness of 35 μm or less.
When both sides of the retardation film have different fracture starting loads in the scratch test, the side with the higher fracture starting load is the first surface and the side with the lower fracture starting load is the second surface.
The polarizing element is a circularly polarizing film characterized in that it is bonded to the first surface of the retardation film. The circularly polarizing film according to claim 1, wherein the fracture starting load on the first surface of the retardation film is 55 mN or more. The circularly polarizing film according to claim 1 or 2, wherein the second surface of the retardation film has a surface functional layer. The circularly polarizing film according to any one of claims 1 to 3, wherein the angle formed by the absorption axis of the polarizer and the slow axis of the retardation film is 35 ° to 55 °. The circularly polarizing film according to any one of claims 1 to 4, which is elongated and has an angle formed by the slow axis of the retardation film and the elongated direction of 35 ° to 55 °. Claims 1 to 1, wherein the retardation film is a stretched product of a resin film molded on a casting body by a solution casting method, and the surface of the resin film on the casting body side is the first surface. 5. The circularly polarizing film according to any one of 5. The circularly polarizing film according to any one of claims 1 to 6, wherein the retardation film is a cellulose ester film. The circularly polarizing film according to any one of claims 1 to 7, wherein the polarizing element, the retardation film, and the protective layer are bonded to each other via an adhesive layer. A circularly polarizing film with an adhesive layer, which comprises the circularly polarizing film according to any one of claims 1 to 8 and an adhesive layer. The circularly polarizing film according to any one of claims 1 to 8 or the circularly polarizing film with an adhesive layer according to claim 9 is provided on the visible side of the optical cell, and the retardation film is closer to the visible side than the polarizer. An image display device characterized by being arranged.

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